Transcript PROCENA STANJA KONSTRUKCIJE AERATORA ZA VODU

CONCEPTUAL DESIGN AND
CONTROL OF BRIDGE
STRUCTURES IN SEISMIC
AREAS
Dr Radomir FOLIC, Professor
Institute for Civil Engineering
Faculty of Technical Sciences
University of Novi Sad
E-mail: [email protected]
INTRODUCTION
 The extensive damage of the recent earthquake
have led to a significant damage of B S`s.
 The cause is often the error of conceptual
design, i. e. the choice of the structural and
foundation system, spacing of piers and
connections between them, deck and abutments,
the spacing of joints, etc.
 This presentation reviews philosophies of seismic
design and protection which can be used in the
conceptual phase of bridge design (Eurocode 8part 2 provisions and recommendations used in
U.S.A. and Japan).
Earthquake—Structure—Response
Taiwan, September 21,1999
Buckling long. bars
caused by bed
confinement
INTRODUCTION
 Beam system is used for small and medium
spans, arch and suspension system for large
spans.
 Importance of structure, site conditions and
regularity of structure influence on methods of
analysis. Based on regularity in plane and
elevation structures are classified as regular or
non-regular.
 Based of the need for the B, to maintain
emergency communications after the design
seismic event, classified: greater than average
(I=1.3); average (I=1.0); less than average
(I=0.7)- (EC 8-2).
INTRODUCTION
 In the most current seismic code aim is
to prevent collapse of the structure
under the design earthquake. The
importance of conceptual analysis in B
designing problems cannot be stressed
enough.
 Choice of appropriate earthquake
resisting structural system (ERS) must
provide in early phase of design.
DESIGN
Three steps in design of bridge structures
(BS) are:
 Conceptual design,
 Analysis, &
Detailing.
Three approaches in design of BS are:
Force - Based Seismic Design FB SD,
Displacement - Based Seismic Design DBD –
(N. Priestley), and
Performance - Based Seismic Design PB SD.
DESIGN
Performance requirements depend on the
importance and configuration-regularity of
bridges (B′s). We can divided (B′s) on:
normal (B′s) & special bridges: arch
bridges, cable-stayed B′s, B′s with extreme
geometry, and B′s with distinctly different
yielding strengths of piers.
Special B′s designed to behave elastically
under the design earthquake or use
seismic isolation to achieved elastic
response.
Elastic and inelastic response (R=q)
Design
Forcereduce
BEHAVIOUR OF B`s IN EARTHQUAKE and
BASIC DEISGN PHILOSOPHIES (BDPh)
The BDPh is to prevent B from collapse during
severe earthquake with small probability of
occurring during service life of the B.
The ductility behaviour using elastic calcul.
with reduced seismic forces (with behaviour
factor q=R) lead to economic solutions.
The alternative is use of elastic systems on
the isolated base or used devices for
dissipation of input seismic energy.
In concrete Binelastic damage located in
the pier and abutments, and plastic hinges
develop simultaneously in as many piers as
possible greater energy is dissipated.
Demand for seismic performance of infrastructures-Japan
BEHAVIOUR OF BRIDGES IN EARTHQUAKE
AND BASIC DEISGN PHILOSOPHIES
According EC 8:
in regions of low and
moderate seismicity
frequently chosen limited
ductile behaviour It is
needed access for
inspection and repair of
the pot. plastic hinges and
the bearings.
In regions of moderate
and high seismicity the
ductile behaviour is
required.
BEHAVIOUR OF BRIDGES IN EARTHQUAKE
AND BASIC DEISGN PHILOSOPHIES
The performance-based crit. to
provide ductile failure  usually
require two level design:
1. to ensure service performance of B
for earthquake with small
magnitude that can occur several
times during service life;
2. is to prevent collapse under severe
earthquake with small probability of
occ. during service life of bridge.
Development of performance-based
criteria is obtained through following steps:
 Establish post-earthquake performance
requirements.
 Determine B specific loads and various
combinations.
 Determine materials and their properties.
 Determine analysis method for evaluation of
demands.
 Determine detailed procedures for
evaluation of capacity.
 Establish detailed performance acceptance
criteria.
BEHAVIOUR OF BRIDGES IN EARTHQUAKE
AND BASIC DEISGN PHILOSOPHIES
 EC 8 seismic resistance (SR) requir. That
emergency communications shall be maintained,
after the design seismic event (SDE).
 Non-collapse req. (ultimate limit state): after SDE
the bridge shall retain its structural integrity, at
some parts considerable damage may occur.
 Deck shall be protected from plastic hinges and
unseating under extreme displacements only
minor damage without reduction of the traffic or
the need of immediate repair. Capacity design
shall be used to provide the hierarchy configuration
of plastic hinges in piers.
CONCEPTUAL DESIGN
 Majority of Codes relates to modeling and
analysis elements and structures (E/S). Only
rarely they deal with conceptual design (Russian
and Swiss).
 Russian Code beam system are recommended.
The arch bridges can be applied only in rock
terrains. In the IXth zone MCS scale precast
concrete, composite-monolithic and concrete
structure bearings is recom.
 Swiss Code local damage - destruction of
bearings or expansion joints tolerated provided
that the superstructure is prevented from falling
CONCEPTUAL DESIGN
Bridges should be as straight as possible. Skew
angle should be as small as possible. Curved
bridges complicate seismic responses.
Vibrations along the axis of a skew bridge cause
torsional response - large rotation demands on
piers heads. In single pier bridges, an eccentricity
between the deck and pier axis would also lead to
torsional response.
Behaviour of continuous B`s is better than other
types. Necessary restrainers and sufficient seat
width should be provided between adjacent
bents at all expansion joints.
Balance mass
and stiffness
distribution
FRAME STIFFNES
CONCEPTUAL DESIGN
 B`s are long period structures - effected
by higher modes.
 Adjacent bents or piers should be design to
minimize the differences in fundamental
periods, and to avoid drastic changes in
stiffness and strength in both longitudinal
and transverse directions.
 Stiffer frame receives greater part of load.
 The pier causing the most irregular effect
due to its stiffness and damaged first
(unequal pier heights) in special situation of
full isolation applied.
CONCEPTUAL DESIGN
It is recommended that:
 Effective stiffness between any two columns
within a bent, does not vary by a factor of
more than 2.
 Ratio of the shorter fundamental period to
the longer ones for adjacent frames in the
longitudinal and transverse directions
should be larger than 0.7.
 Balanced mass and stiffness distribution in
a frame results in a good response.
Irregularities in geometry increase complex
nonlinear response.
Unfavorable distribution of transverse
seismic action
Permissible
Earthquake
Resistance
systems -ATC
Permissible
Earthquake
-resisting
elementsATC
require owner's
approval - ATC
require owner`s
approval - ATC
Earthquake-resisting elements that are not
recommended for new bridges- ATC
Methods of minimizing damage to abutment foundation
ATC
Location of primary plastic hinge, a) conventional
design, b) menshin-seismic isolation design, c)
bridge on a wall type pier (Japan Code 1996)
MODELING AND ANALISYS
MODELING AND ANALISYSwithout base isolation
MODELING AND ANALISYSWITH BASE ISOLATION
PROTECTION OF BRIDGE STRUCTURES
 Concrete B design to direct inelastic
damage into columns, pier walls, and
abutments.
 The superstructure should sufficient
over-strength to remain essentially
elastic if piers reach plastic M capacity
 Seismic protection devices-energy
dissipation and isolation at approp.
location provide good behaviour.
PROTECTION-CONROL OF BRIDGE
STRUCTURES
Spri
-ng
Spring
Bridge control system – devices, advantages and
disadvantages
BASE ISOLATION
FRICTION DAMPER
Deformation response spectra/with variation
damping ratio  for SDOF system
Pseudo-acceleration spectra
peak value of A(t)
CONTROL OF STRUCTURES
Mxt   Cxt   Kxt   Dut   Df (t )
Three-span C. Frame B. S. of MDOF ex. b) Long. Degree of freedom,
c) Tran. DOF,d) rotational DOF, e) mode shape I, f) mode shape 2, g)
mode shape 3.
WITHOUT PROTECTION
Three span
bridge with
active control
system (a); b)
B model for
analysis; c)
SDOF system
controlled by
actuator
Controllable sliding bearing
Base isolation + Active control
Simple-span bridge with hybrid control system &
b) lumped mass system model; c) four-degreeof-freedom system
Multi column structures offer the option of fixed or
pinned base solutions. Displacements at the deck level
are reduced, especially in the transverse direction.
Options for
lateral force
resisting
systems
Monolithic connections between deck and abutment are more
commonly used for small bridges, solution b) is more reliable
Than of a). Bearing supports have many configurations c) and d).
For both configurations the bearings may be substituted by isolators.
Options for
abutmentdeck
connection
Mechanisms
of resisting
forces at the
abutment
For piers the circular section is desirable (L & T demands are
similar) provides uniform confinement and restrains the L
bars from buckling. In the rectangular sec. the protection of
long. bars against buckling must be provided with add. S & tie.
DETAILING-CONNECTIONS
Comparative provisions for
aseismic design
Provisions Caltrans (USA)
Eurocode 8
Japan
1.
Performance
Criteria
Structural integrity to
be maintained and
collapse during strong
shaking to be prevent.
No collapse under safetylevel event (ULS). No
damage under frequent
earthquakes (SLS).
To be maintained in
small and moderate
earthquakes (EQ).
Collapse to be avoided
for large EQ.
2. Design
philosophy
Adequate duct.
capacity to be
provided and failure of
non-duct. el. and
inaccessible to be
prevented.
Sufficient strength of
elastic str. In order to
avoid damage. Brittle
types of fail. To be
avoided in all structures.
Component to
perform elastically
under functional
earthq. Detailing
specific components to
avoid damage
3. Design
approach
Single-level design.
Desired perf. at lower
earthquake load is
implied.
Single-level design.
Desired performance at
lower earthq. load is
implied.
Utility level earthq.
and working stress.
Detailing to avoid
collapse of girders
shacked. All review.
CONCLUSIONS
 The basic philosophy for seismic design of
ordinary bridges is that for small to
moderate earthquakes the bridges should
resist within the elastic range without
significant damage, while for large earthquake
must prevent collapse.
 In current design practice the changes are
necessary to incorporate improved design
procedure, especially Perf. B S D.
 It is very important to analyse plane layout
and layout in elevation of BS in preliminary
phase to respect presented recommendations.
References
 ATC, Improved Seismic Design Criteria for California bridges: Provisional Recommendations,
ATC - 32, Applied Tech. Council, Redwood City, CA, USA, 1996;
 AASHTO (American Association of State Highway and Transportation Officials): Bridge Design
Specifications, 1998.
 Bridge Engineering-Seismic Design (BESD) Ed. W. F. Chen and L.Duan, B. R. 2003.
 CALTRANS (California Department of Transportation) SEISMIC DESIGN CRITERIA, VERSION
1.2, (p.121), December, 2001
 Duan, L., Wai-Fah, C.: Bridges, in Earthquake Engineering Handbook, Ed. W.F. Chen and C.
Scawthorn, CRC Press, Boca Raton, 2003. pp. 18.1-18.56.
 Duan, L., Li, F., Seismic Design Philosophies and Performance-Based Design Criteria, (p. 5.15.35) in BESD, Ed. W. F. Chen and L. Duan, CRC, B. Raton, 2003
 Elnashai, A., Seismic Response and Design of Bridges, in Manual of Br.Eng., 2002.
 EC8/2 – Eurocode 8: Design of Structures for Earthquake Resistance – Part 2: Bridges, prENV
1998-2, May 1994, CEN, Brussels.
 EC8/2 – Eurocode 8: Design of Structures for Earthquake Resistance – Part 2: Bridges, prEN
1998-2:200X/ Draft 5 (pr Stage 51) June 2004, CEN, Brussels.
 Folić R., Lađinović Đ.: Some current methods and tendency in seismic design of concrete
bridges. Proc. of the 5th International Conference on Bridges Across the Danube, Novi Sad,
Serbia & Montenegro, 24-26 June, 2004, Volume II, 133-144.
 Pristleey, J.M.N., Seible,F. and Calvi,G.M.: Seizmic Design and Retrofit Bridges, Wiley
Interscience, New York, 1995.
 Regulations for Seismic Design a World List-1996, Supplement IAEE, 2000&2004.
 Troitsky, M.S.: Conceptual Bridge Design, in Bridge Engineering Handbook, Ed. W.F. Chen and
L. Duan CRC Press, Boca Raton, Florida, 1999. Chap. 1. pp 1.1-1.19
 UNJOH, S., Seismic Design Practice in Japan, (p. 12.1-12.37) in BESD, Ed. W.F. Chen and L.
Duan, CRC, Boca Raton, 2003.